First, if you give specific dimensions, there usually has to be a good reason for them- like say, denoting the minimum safe distance from an area-of-effect property the SCP has.

Second…

SCP-XXXX is a mushroom that has branched off from the Termitomyces titanicus fungus, native to ██████, Africa,

… needs some clarification. It looks like you're censoring the location if the species named, which is counterproductive. Armed with the name of the species and size of the blackbox, I can use google to bypass the censoring (it's Zambia, BTW).

Aside from that, you need to (obviously) finish the draft, since I can't say how well it will do at this stage.

The dimensions of the terrarium and the room around it is simply to the "creatures" room to move about comfortably, and of the room for the personnel to move about comfortably to maintain the habitat. The material's used is to provide a slick surface on which they cannot "crawl" on, preventing containment breech, which if it were to occur, well, I'll leave that for later

SCP-XXXX is to be kept in 5m x 5m x 1m acrylic terrarium installed with a sufficient drainage system, within a 6m x 6m x 2.5m steel room installed with an irrigation system capable of simulating the rain patterns of Zambia, as well as a drainage system to prevent flooding.

This is just one sentence! That's pretty long, I suggest splitting it into two seperate ones.

Materials for containment is used

Materials are used, or material is used.

is used for it smooth/slick surface

What is 'it' doing there? Should be 'a'?

to prevent any organisms from "crawling" out.

You could just say 'escaping' or 'breaching containment'.

When the numbers of XXXX exceeds the capability of the habitat to support organisms, all but 1 instance are to be disposed of by incineration.

Don't refer to your SCP as 'just the number'. Use SCP-XXXX or it.

consistent with the vegetation of Zambia.

How does this look like? Is every personnel fully aware how the vegetation of Zambia looks like so that they can detect differences if they occur?

As long as this procedure is followed, no containment breach will occur.

No, you just said you also need to incinerate exceeding instances of SCP-XXXX. By reading this line it sounds like trimming the bushes is all you need to do, which makes the previous statement of incineration redundant.

located in locker

located in a/the locker

SCP-XXXX is a mushroom that has branched off from the Termitomyces titanicus fungus, native to Zambia, Africa, that grows on corpses at the beginning of the rainy season, which can grow a cap up to 1m in diameter on a stipe up to 57cm in length.

Once again, very long sentance. Split it up.

XXXX resemble the titanicus genus,

Resembles? And, I've mentioned this already but as a reminder, use SCP-XXXX instead of just XXXX. Also why is this the beginning of a new paragraph? You're still describing its appearance.

While immobile, this creature

Use SCP-XXXX or it.

stand erect.

Don't most mushroom fungi stand erect? You already described how it uses a stipe.

While on the hunt

This sounds like it's stalking its prey, but you said it is an immobile fungus. I think you should change it to something like 'SCP-XXXX can emit a sweet aroma to lure prey…'

Also, which organisms are affected by this aroma? Humans, insects, mammals? And can SCP-XXXX eat prey bigger then itself?

immobile from its sap

Wow, what!? I just read it is 'coated with sap' and now it suddenly has a paralyzing effect? Why didn't you describe that?

the stomach sucks up into its body,

Sucks it/the prey/the subject up.

XXXX is capable of movement, traveling at speeds up to .3m/hr

But earlier you said it was immobile!? Is its primary state immobile, but it can move as well?

allow it to climb surfaces (in combination with its stomach sap)

I assume it's because the sap is sticky, but it could've been better explained.

some sort of texture, i.e. bricks, trees, wood, etc.

Changing this to something like 'SCP-XXXX can climb any kind of surface, regardless of texture' makes it sound more professional.

Discovery

The discovery file is very short and doesn't provide anything, but I assume you're still working on that?

Ok, so all in all the needs a lot of work to make it finished. You should focus on the writing first. The way you've built the description is very weird: first you describe how it looks like, then in a new paragraph you continue to describe how it looks like, then you talk about its behaviour, afterwards you return to describe how it looks like again and finally continue with its behaviour again. Put texts of the same subject (behaviour, appearance etc.) in the same paragraphs and after eachother. Also the writing style sometimes sounds very professional (like the Foundation wrote it), and sometimes just not. Try to fix that as well, if you read carefully you'll see which areas need some work (I've already highlighted some in the feedback).

The idea of the SCP is kind of 'meh' to me. In my mind it's a colorful mushroom version of the Venus Flytrap, which hapens to also move. Add some story to this SCP and make it so that the abilities make sense! Don't add some weird abilities to this thing just because it looks cool, it should make sense why it has those abilities together.

I suggest you also read about some other plant SCP's. They may not be similar to yours, but they can certainly help you figure out how to approach your SCP's abilities and such. Here are some examples (as I said, not similar to yours, but plants as well):SCP-038SCP-143SCP-386

Anyway, I hope I've provided you with some useful information and good luck on editing! :)

I believe I said that when it wasn't mobile, and not that it was entirely immobile, but I was at work dodging supervisors and directors so I could have been in error. I will check it out later.

And the sap is not a paralyzing agent, just super sticky like a glue board used to catch rodents and small critters.

Also, it will be getting weird, this is just the surface. I will also include some footnotes to explain some things. I actually have some co-workers that frequent the SCP series, and have been getting feed back from them as well. They have more information on it than what has currently been posted.

I have to leave in 30 min….don't want to get lost in editing….if it is slow at work today, I will take all of your advise into consideration, and utilize what makes sense to me. Ill PM you once I am done with the next set of edits if you don't mind.